Polyvalent Vaccines Using Vaccinia Virus Are Highly Favored by Doctors

Polyvalent vaccines using vaccinia virus are highly favored by doctors and physicians but are especially challenging for those who develop them, because

A) coat proteins form a relatively rigid structure and do not allow much space for additional proteins to be expressed.
B) multiple foreign proteins simultaneously synthesized often disrupts each otherʹs activity.
C) vaccinia and most other viruses engineered for vaccines contain only one restriction site for cloning in their genome.
D) virus genetic manipulation uses transfection, which is an inherently inefficient process.